Teachers' headshots are being superimposed on to pornographic images in some of the worst cases of social media misuse, a union chief has claimed.

Jacquie Reid, deputy general secretary of the Ulster Teachers' Union, was speaking before its annual conference yesterday in Newcastle, Co Down.

She also claimed there have been cases where parents have waged campaigns against teachers on social media.

She has called for the Department of Education to issue clear guidance to teachers on how to protect themselves online.

"Initially, we had been working with the employing authorities and the Department of Education on the whole area of social media and what standards were to be expected from teachers regarding their personal use of things like Facebook," she said.

"However, as the discussions progressed we soon realised that rather than legislating for what teachers can and can't do on social media, teachers actually needed protection against damaging campaigns orchestrated against them by parents and pupils.

"In one of the worst cases I've heard of, teachers' faces were transposed on to pornographic images then uploaded onto social media and distributed. Once it is published, it's very difficult to pull it back and the whole education community suffers.

"We have also had cases where parents mount campaigns against staff on social media. In one such case, parents were highly critical of a principal on Facebook and while they named neither the principal nor the school, because it was such a small community everyone who read it knew who they were talking about.

"Every school in Northern Ireland has a policy regarding the safe use of the internet by pupils - now we need something to protect teachers, too, and we would call on the Education Authority and the department to address the issue sooner rather than later.

"The vast majority of abuse is quite low level. Often it's issues that parents would normally raise through the official channels at school. Instead, what they're doing is putting it up on Facebook, that just seems to be a feature of our society. It ranges from pointed comments about people to serious allegations suggesting inappropriate conduct by teachers.

"There's also been cases of pictures of colleagues' heads put on pornographic films.

"In these cases I would advise teachers to contact the schools directly, but of course the material is already out there. No matter how much teachers deny things, they're afraid people will think there's no smoke without fire."

She added: "We've had teachers who've left the profession due to the stress. It's still relatively rare, but the difficulty is in keeping on top of it all."